1. Field of the Invention
Embodiments of the present invention generally relate to power generation, more particularly power generation incorporating combustion, such as internal combustion engines, including power generation wherein it is desirable to reduce the emission of oxides of nitrogen, hydrocarbons, carbon dioxide and particulates. More particularly still, embodiments of the invention include power generation using a power source having a regeneration mechanism, whereby emissions from combustion are recovered for reuse as a source of fuel for the power source. Additionally, the power generation methods and apparatus herein may be used to provide solar generation capability.
2. Description of the Related Art
Power generation employing internal combustion engines is traditionally accomplished by introducing fuel typically a hydro-carbon based fossil fuel or distilled hydrocarbon fuel) and air into a combustion chamber or volume, and igniting or exploding the fuel, in the presence of oxygen supplied in the air, to cause expansion or increased pressure in the chamber, thereby causing relative movement of a combustion chamber component. The movement of the combustion chamber component is employed to cause a consequent output from the engine, typically in the form of torque and rotation of a shaft extending therefrom. For example, in a piston type of engine the increased pressure caused by the combustion of the fuel-air mixture causes movement of a piston in piston housing, and the piston is connected, through an arm, to a rotatable crankshaft. Likewise, in a gas turbine style of engine, the fuel-air mixture is combusted in a combustion chamber, and the expanding gaseous result passes through a plurality of rotationally mounted finned rotors, causing them to rotate with torque. The result is rotation of a shaft, such as a shaft upon which these the rotors are mounted, the shaft being coupled to a generator, a vehicle or the like, to power the generator or vehicle.
In such internal combustion engines, the efficiency of the engine, as measured by power output on the shaft as compared to the potential power provided by the fuel, is on the order of 30% to 60%. The difference between actual energy recovered and potential energy available, i.e., the 70% to 40% loss in efficiency, is a result of several factors, including inadequate or incomplete combustion of the fuel, generation of wasted heat, frictional losses in the mechanisms used to transform the chemical energy released in combustion to physical energy in the output shaft, exhausting of the combusted mixture before complete recovery of the energy thereof, etc. Each of these factors adds to yield a relatively inefficient internal combustion engine.
One mechanism that has been used in the past to increase the efficiency of the fuel use has been to use the heat remaining in the exhaust to either generate heat for building heating purposes, or to generate further power through a steam turbine, or the like. For example, the temperature of the exhaust of a gas turbine is sufficient to heat and often to superheat steam, which may then be passed through a steam turbine for energy generation therefrom. Thus, the energy recovered in the output of the steam turbine is added to that recovered by the gas turbine as a measure of efficiency. However, gas turbines as a primary engine and without a method of secondary heat recovery are less efficient than diesel cycle engines, which are currently, on a stand alone basis (i.e., no secondary heat recovery based power generation) the most efficient engines commercially available. Further, engines operating on the Stirling cycle would theoretically be more efficient, but have never gained commercial acceptance. The relatively efficient diesel engine using commercial fuels has an exhaust temperature insufficient for efficient steam turbine power generation therewith, whereas the gas turbine has high enough combustion temperature, and exhaust temperature, to allow sufficient heat recovery for commercial uses. The gas turbine with such a heat recovery system is currently the most efficient commercially available system for combustion based electricity production.
Several methods have been used or proposed to increase the efficiency of the internal combustion engine itself. One such methodology includes modifying the air used for combustion by enhancing the oxygen percentage thereof. As a result, a greater percentage of oxygen is available in a given volume of air-fuel mixture (as oxygen displaces Nitrogen in the air), resulting in the ability to have a greater quantity of oxygen and fuel in the mixture per unit volume, and a resulting higher combustion temperature. As is known that if the temperature of the combustion reaction is increased the resulting efficiency of the engine should increase, various schemes have been proposed in the past to provide such an increase in both temperature and efficiency. For example, it is known to combine or mix additional oxygen with the air intake of an internal combustion engine, with a resultant substantial increase in energy recovery efficiency. Further, emissions of carbon monoxide, hydrocarbons and particulates were substantially decreased. As naturally occurring air has an oxygen content of about 21%, the added oxygen both raises the combustion temperature and increases the total quantity of fuel combustible in a combustion chamber of a given size. For example, adding sufficient oxygen to air so that the resulting mixture is 35% oxygen, and employing a diesel cycle engine and diesel fuel, has been demonstrated to result in significant increase in power output for an engine, as the greater concentration of oxygen allows greater quantity of fuel to be introduced and combusted. However, the engine also released, as exhaust, unacceptably rich emissions of greenhouse gasses as nitrogen oxides, approximately double that of a non-oxygen enriched diesel cycle engine, and also was unable to be effectively controlled. Although the amount of Nitrogen in the oxygen enriched air is less (because, on a volume to volume comparison, some is replaced by oxygen) and thus one would expect fewer NOx emissions, the increased temperature caused a higher reaction rate or reactivity between nitrogen and oxygen, resulting in a greater efficiency and power output, a lower emission of particulates, CO and other compounds, the production rate of NOx compounds also was significantly increased. As a result, this concept has not been further pursued.
An ongoing issue with the use of fossil fuels or other hydrocarbons in conjunction with internal combustion engines is the generation of pollutants, such as NOx or COx compounds. A portion of these emissions, specifically the NOx compounds, are known to cause disruption of the ozone layer, and/or smog, as well as being generally unhealthy when inhaled. CO is toxic, as is an additional emission gas, CHx, Likewise, CO2 has been implicated in global warming, and the emission of it may become limited in the future. Thus, although the efficiency of the engine can be increased, the resulting pollution is unacceptable.
An additional method of power generation is solar power, such as a solar energy generating station or “SEGS,” in which solar energy is converted to electricity. As solar energy is unavailable during the night, such SEGS plants are typically used to generate “peak” and mid peak power, i.e., they are used during periods of the day when the sun is shining when electricity demand is highest. These peak times are locale dependant, such as, for example, locations of high solar insulation where the need for electricity to power air conditioning units is much higher in summer months. Alternatively, or additionally, such peaks can occur as electrical consumers return to their homes in the late afternoon or early evening hours, and begin using air conditioners, appliances and the like. To provide the peak power needed, utilities are often willing to pay an a higher charge to the power generator, including SEGS, for this power during peak hours. Further, these peak plants are often operated only during peak demand periods, and thus their cost, i.e., the investment in infrastructure, is not recoverable based upon continuous generation, but rather based on less that full utilization.
Although SEGS have proven to be capable of providing power during peak operation times, there are limits of competitiveness which affect their use for base line power generation needs. As the plants cannot operate in non-daylight hours, the cost of building the solar power generation equipment must be justified based solely upon generation during these daylight hours. Thus, the electricity generated must be capable of being sold at a premium over electricity generated at power stations where the power generation is continuous, i.e., base line plants which operate continuously, 24 hours a day, except when down for maintenance or unusual lack of electricity demand. In localities that have significant disparities between base load and peak load, it is not uncommon for peak load to be 2 to 6 times larger than base load requirements. In these localities with big disparities between base load and peak demands it is important to encourage building peaking plants that do not run many hours and this incentive is usually provided by providing substantially higher prices or values on peak pricing. Even with substantially higher priced peaking power it is usually the case that economic analysis will determine that it is most beneficial to the energy supplier to meet these requirements with the lowest cost, typically less efficient and more environmentally unfriendly systems than solar. In order to encourage clean energy sources to supply this peak power, incentives are sometimes offered. The incentives often give clean a energy supplier delivery preferences either by accepting clean energy on a first priority basis against other suppliers if they are priced equally, or to allocate some percentage of peak or as delivered energy to be supplied from clean energy sources. As well as the delivery preference a tax environment of specific SEGS benefits are often provided to make of an even tax playing field between SEGS suppliers and fossil fuel plant providers. As a potential supplier of clean energy, SEGS plants, which are based on the delivery of solar thermal sources of energy, are in an unusual position. On one hand they are able to deliver clean energy from solar and they are also able to produce energy by using fossil fuels to power a steam turbine otherwise normally powered from solar energy. Were the SEGS to receive preferences associated with its clean solar delivery it is usual practice to limit the amount of fossil fuel energy the SEGS plant is entitled to produce relative to the solar energy that it produces and requires the plant to produce 100% of its output capacity from solar energy alone.
Solar energy plants which often deliver energy during peak demand hours typically provide that energy as a direct consequence of the amount and intensity of the solar incident light that falls on the solar field, with the solar field being comprised of photovoltaic fields or solar thermal fields. However solar thermal fields have an added flexibility. Solar thermal plants typically operate by raising the temperature of some intermediate fluid to high temperature and then circulate that intermediate fluid through a heat exchanger that boils water, and resultant steam is used to run a steam turbine to make electricity. However it is technically quite easy for the solar thermal steam to be provided by fossil fuel and not just from solar source. Thus when the sun is not shining, the power block portion of the solar thermal plant is able to operate by using fossil fuel to directly heat the water in a parallel boiler, creating steam to run the turbine. This added flexibility allows solar thermal plants to be available to supply energy when the sun is available and when the sun is not available. However, because of the limitations on the use of fossil fuels and the requirement that the plant must be able to produce 100% of its rated output from solar alone to receive preferential supply status and certain tax and other benefits of being considered solar, the fossil fuel based generation is minimally used and sub-optimum power generation equipment is used. For example, although it may be reasonable to combine gas turbine and solar generation, the cost effective solar plants available before this new technology are not able to produce for technical reasons the full rated power of the plant from solar alone. Thus a current SEGS plant cannot operate highly efficient combined gas-steam cycle turbines and still be considered a solar plant in many if not all locales. Most solar energy equipment at most can heat an intermediary fluid converted to steam and drive a turbine to temperatures of about 400° C. Whereas, in order to run a highly efficient combined gas-steam turbine, where the waste heat exiting the gas turbine is fed into the steam turbine, the initial temperature of the compressed air entering the gas turbine must be heated to 2000° C. 1600° C. needed to bridge this gap results in commercial solar fields running the most efficient steam turbines at approximately 40% efficiency instead of the most efficient combined cycle plant running a 60% efficiency. There does exist one type of solar collector technology called a power tower, which focuses a large number of mirrors, each one independently shining the sunlight onto a small location at the top of a very tall tower. That location at the top of the tower becomes very hot, in excess of 2000° C. The goal of this design was to be able to obtain temperatures that would be able to run efficient combined gas-steam turbine systems. However for many reasons most of which can ultimately be related to lack of sufficient material technology at this stage this approach is too expensive, inefficient and unreliable to be developed in to a commercial product. Further improvements at the material science level that may take many years to develop must still made.
Therefore, their exists a need in the art for a power source, particularly one using a combustion based engine, wherein the resulting efficiency is increased without the production of, or with a significant reduction in the production of, byproducts such as NOx and CO and particulates in the resulting emission stream, and with greater efficiency than prior art devices. Likewise, there is a need to provide solar based generating capacity (SEGS) having more widespread use, significant increases in efficiency, and significant increases in valuable on-peak delivery of energy and power compared the amount of energy and power delivered off peak. All the above being achieved within frameworks that are consistent with restricted fossil fuel use.